Abstract Charcot-Marie-Tooth (CMT) diseases are the most common form of hereditary peripheral neuropathies, affecting approximately 1 in 2,500 people equating to approximately 125,000 people in the United States. No effective therapy for CMT currently exists. The diseases specifically affect the peripheral nervous system and are characterized by progressive motor neuron degeneration, muscle atrophy, and sensory loss. Recent progress in neurogenetic studies has uncovered aminoacyl-tRNA synthetase as the largest gene family implicated in CMT. Among them, GARS, encoding glycyl-tRNA synthetase (GlyRS), is the first member identified and whose mutations cause a dominant axonal form of CMT (CMT2D). Despite the broad requirement of GlyRS for protein biosynthesis in all cells, mutations in this gene cause a selective degeneration of peripheral axons leading to deficits in distal motor function. The goal of this project is to determine the disease-causing mechanism for CMT2D. Our central hypothesis is that CMT2D-causing mutant GlyRS acquires an aberrant binding activity that directly antagonizes an essential signaling pathway for motor neuron survival, and that the toxic function of mutant GlyRS may be linked to a dysregulated, extra-translational function of wild-type GlyRS. Our hypothesis is based on our results from the previous funding period of this grant and from our collaborations with other laboratories. Through a broad range of methods from hydrogen-deuterium exchange analysis, X-ray crystallography, biochemical, and cell-based analysis to mice studies, this project will not only shed light on CMT2D causing mechanisms and open doors for developing therapeutic strategies for CMT2D patients, but also reveal important regulatory functions of GlyRSWT beyond its classic enzymatic function in protein synthesis.